Her rare Null ability cancelled out any magic done around her. So any trace charms sent out by Tony's goons couldn't locate Cassie. But that also meant that Tammy couldn't teach Cassie how to do magic—which requires practice—so Cassie never learned.

The purpose of this section is to be able to find things in the series. Please use References. This section may have spoilers. If you want to avoid spoilers, please don't read the summary for a book that you have not read yet. Think of the book title as a "Spoiler Warning".